Project 2 will investigate the role of immune responses in dictating the course of BRAF mutant melanoma and how such knowledge can be exploited to develop effective combination therapeutic regimen(s) based on synergy between immunomodulatory molecules and drugs targeting oncogenic BRAF. Expression of immunoregulatory molecules associated with responsiveness and resistance to BRAFtargeted therapy in human and murine melanoma will be determined using molecular, immunohistologic and flow cytometry approaches. Because of the recent therapeutic promise of anti-CTLA-4 therapy in melanoma. Project 2 also will analyze how ahti-CTLA-4 therapy alters the tumor microenvironment in samples from patients with melanoma treated with this immune checkpoint modulator. Functional and clinical validation studies of immunomodulatory targets in BRAF-mutant melanoma initially will determine how BRAF-targeted therapy impacts anti-tumor immunity using human PBMCs and TILs from treated patients and IBIP mice in the settings of responsiveness and resistance to BRAF therapy. Further studies will explore the impact of blocking immunomodulatory targets individually and in combination therapeutic strategies with BRAFtargeted therapy on tumor regression and anti-tumor immunity. Initial functional studies will focus on the CTLA-4 and PD-1/PDL pathways because of their potent immunomodulatory effects in melanoma. This detailed characterization of the immune response in BRAF mutant human and mouse melanomas during tumor growth, treatment and resistance will provide molecular insights into the immune components of BRAF-targeted therapy and guide development of rational combinations of BRAF-targeted therapy and immunotherapy to minimize resistance and achieve durable remission.